Continuously actuatable keys pertaining to a keyboard comprising an integrated signal detection element, and method for signal processing

ABSTRACT

The aim of the invention is to develop a keyboard for compact mobile electronic appliances, said keyboard comprising an integrated signal detection element and enabling simple data input and simultaneous continuous control possibilities using a plurality of keys; an electronic inquiry mechanism for actuating the keys; and an evaluation method for a momentary key position during the continuous actuation of individual keys. To this end, keys which are applied in a mobile manner and provided with a spring suspension are mechanically coupled, on the lower side thereof, to a continuous strip conductor extending over at least one key and having a high electrical resistance, such that when the keys are actuated, the strip conductor comes into contact with another strip conductor, in the actuation position, said other strip conductor extending over all of the keys and having a low electrical resistance, and an analog-digital converter ADO determines the electrical resistance or voltage drop between the strip conductor and an end of the strip conductor, said measuring value being unequivocally associated with a defined key and the actuation position on said key.

The invention relates to a keyboard with maneuverable keys that can bepressed and tilted and that are equipped with a signal detection elementthat registers the key actuation, and a method to translate theelectrical impulses initiated by the key actuation into signalsidentifying the position of the actuation by detecting the force andposition of the key actuation.

According to the state-of-the-art, keyboards and input devices forcursor control are typically conceived as separate units, so that theircombination requires double evaluation electronics and software.

With notebook computers, for example, a little joystick is frequentlymounted near the space bar in order to control the mouse pointer. Thisjoystick can be implemented e.g. on the basis of strain gauge. As analternative, a flat sensor on capacitive basis is frequently used formouse control. In both cases, the technical effort to evaluate thecomplex signals is significant.

With mobile phones that include organizer functions, so-called smartphones, a solution is known where a flap keyboard is mounted onto atouch screen. If the device is used for data input, then the keys can beplaced on the touch screen and any key actuation will then actuate aspecific position of the touch screen. This saves separate electronicsfor the key evaluation. However, the flap keyboard only allows to useeither the keyboard or the touch screen at one time.

There also numerous proposals to extend keyboards as e.g. the U.S. Pat.No. 5,973,621 (David Levy 1999) or the U.S. Pat. No. 5,528,235 (EdwardLin 1991). Such extensions on the basis of electrical switches aremechanically costly and vulnerable and have not prevailed as a result.

It is a known technique to code keys with analog values by means of avoltage divider (FIG. 19). A specific voltage can be metered at each ofthe resistors R1, R2, R3 and R4. When one of the pushbuttons S1, S2, S3or S4 is pressed, this voltage is led to the analog/digital converter(AD). As long as no pushbutton is pressed and thus no contact closed,the AD meters a positive voltage due to the pullup resistor Rp.

This allows to scan the whole keyboard with only two or three cables.While the cost for the leads is lower, there is higher cost for thedecoding by means of the analog/digital converter. For these reasonsthis technology is typically limited to those cases where the lower leadcount brings a significant advantage.

Another known technique is the foil potentiometer (FIG. 17, sectionview). In their simplest form they consist of a strip of flexible foil51, which is partly coated with a material with a high electricalresistance (between 100 Ohms and approx. 500 Kiloohms per 10 cm) such asgraphite 53, and a second foil 71 that is partly coated with a materialwith a low electrical resistance 72 such as silver (less than 10 Ohmsper 10 cm) and thirdly a spacer 61 that keeps both foils at a distanceof approx. 0.02 mm up to 1.0 mm during their resting state. The spacer61 exhibits an opening 211 which allows a contact between the conductivecoatings 53 and 72 when mechanical pressure is applied. At the edge ofthe foils 51 and 71, the coatings are connected to the electrodes 202and 203 (FIG. 20, view from above). Another electrode 222 is located atthe coating of foil 71 (FIG. 22, view from above). The electrodes allowa contact with the evaluation electronics. When actuated (FIG. 18) theflexible foil 51 is slightly bent at the touched position, so that thespacer 61 is bridged and an electrical contact between 53 and 72 iscreated. The electrical resistance between the electrodes 202/203 of theresistively coated foil 51 on the one side and the electrode 222 on thefoil 71 on the other side is now proportional to the distance betweenthe contact point and their ends.

If the foil potentiometer is connected as a voltage divider (FIG. 23),then the voltage metered at the analog/digital-converter AD isproportional to the position of the tap point.

Alternatively, both the actuation point and the length of the restingsection may be determined. To this end, a voltage is applied at theelectrode 222 and the Ohm's resistance between the electrodes 202 and203 is measured. Both measured values correspond to the distance to bothends, whereas the sum of both measured values subtracted from the totalresistance between 202 and 203 correspond to the length of the restingsection. This is because actuation on a section or on two points insteadof a single point creates a short circuit between both points, whichreduces the resistance between 202 and 203 proportionally correspondingto the distance of these points. This is also state-of-the-art in thearea of foil sensors.

While foil sensors allow a continuous adjustment in a simple manner,they do not deliver any tactile feedback due to their flat form factor.Therefore they do not offer a comfortable data input like ordinarykeyboards and have only enjoyed limited success.

The goal of the invention is to reduce the cost of mobile electronicdevices that have keys as input elements, by reducing the volume and theweight, the number of parts as well as the energy consumption, andsimplifying the operation, where the keyboard must be robust againstrough transport conditions and manufacturer's tolerances.

The invention is based on the task to develop a keyboard that issuitable for the employment in compact mobile electronic devices with anintegrated signal detection element, that allows data input withunlimited comfort and at the same time a continuous control for aplurality of keys, interrogation electronics for the keyboard actuationand a method to determine the current key position with a continuousactuation of particular keys.

The task is solved by the features described in the independent patentclaims.

The invention will be demonstrated by means of an example. The figuresare as follows:

FIG. 1: circuit diagram of a keyboard for voltage measurements with anAD converter according to the invention

FIG. 2: circuit diagram of a keyboard for resistance measurements withtwo AD converters according to the invention

FIG. 3: circuit diagram of a keyboard for resistance measurements withthree AD converters according to the invention

FIG. 4: circuit diagram of a keyboard for voltage measurements and twocalibration electrodes according to the invention

FIG. 5: upper foil of the signal detection element with printedconductive paths

FIG. 6: middle foil of the signal detection element with punchedopenings

FIG. 7: lower foil of the signal detection element with printedconductive paths

FIG. 8: example of key caps with labels

FIG. 9: upper foil of the signal detection element with printedconductive paths

FIG. 10: middle foil of the signal detection element with punchedopenings

FIG. 11: lower foil of the signal detection element with printedconductive paths

FIG. 12: example of key caps with labels

FIG. 13: key with actuator (cutaway view)

FIG. 14: slightly pressed key (cutaway view)

FIG. 15: strongly pressed key (cutaway view)

FIG. 16: pressed and tilted key (cutaway view)

FIG. 17: architecture of a foil potentiometer (cutaway view)

FIG. 18: foil potentiometer, actuated state (cutaway view)

FIG. 19: keyboard encoded with resistance cascade

FIG. 20: foil potentiometer, upper foil

FIG. 21: foil potentiometer, middle foil

FIG. 22: foil potentiometer, lower foil

The solution is to mount a signal detection element, e.g. a foilpotentiometer underneath a group of maneuverable keys in such a way thata pressed key can be assigned a specific electrical resistance at theelectrodes of the foil potentiometer. The tilt of a key resp. a variabletouch position on the key leads to a variable contact point and thus toa change of electrical resistance. However, if no key is pressed, thenno electrical contact between opposite electrodes is established.

Additionally, the applied force on each key can optionally be determinedby measuring the reduction of total resistance of the foilpotentiometer. As a higher force on a key is accompanied with adeformation of the soft key underside, a longer resting section and acorrespondingly reduced total resistance, the applied force can bederived from the difference of the resistance.

Assuming a sufficient accuracy of measurement, a huge number of keys aswell as their actuation position can be interrogated in this manner witha single foil potentiometer. This requires only a small number of leads(a minimum of two without force measurement, three with forcemeasurement).

FIG. 1 shows the circuit diagram of a keyboard according to theinvention. P1-S1, P2-S2 etc. constitute units each: A key actuationcloses e.g. the contact S1 and the resistance of the potentiometer P1results from the actuation position. Rp is a pull-up resistor whichpulls the input of the analog-digital-converter AD to a defined valueduring the contactless resting state. The foil potentiometer composed ofP1 to P4 corresponds to voltage divider, so that the AD convertermeasures a voltage that relates to a specific key and actuationposition. The example exhibits four keys, but it would be the same forany other number of keys.

FIG. 2 shows how the same keyboard can be evaluated with a differentmeasuring assembly. With an additional AD converter it is possible todetermine the force that is applied on a key. A stronger force deformsthe soft key underside and thus creates a longer resting section on thefoil potentiometer, i.e. a section with a short-circuit. Now theelectrical resistance between the actuated key S1 to S4 and AD1 and AD2is measured by means of the AD converters AD1 and AD2 and is compared tothe total resistance from P1 to P4 during the resting state. Thereduction of resistance is exactly related to the short-circuit section,thus the resting section of the soft key underside and thus to theapplied force.

FIG. 1 and FIG. 2 demonstrate arrangements where the continuousactuation of arbitrary keys on a single axis is evaluated. Thiscorresponds to a movement to the side of the actuation position or thetilted actuation of a key.

FIG. 3 shows how an evaluation is also possible along two axes forselected keys, if additional AD converters are available. In this case,P1 a and P1 b constitute two potentiometers that are controlled by asingle key (FIG. 12, element 121). Three measuring points at the edge ofa circle are sufficient to determine the focal point of contacting;namely that point on the circle area that has the calculated distance tothe three measuring points.

In order to increase the reliability and precision, it is possible toallow for reference points at one or more points of the keyboard. OnFIG. 4, CAL1 and CAL2 serve as calibration values for measurement withan AD converter; the value of CAL1 lies directly between P1 and P2,while the value of CAL2 lies directly between P2 and P3. The calibrationcan be performed as long as no key is actuated. The reference pointsshow precisely a relative proportion to the key actuations, even if thetotal resistance might vary due to temperature changes etc.

It is possible to use a foil potentiometer as a signal detection elementof a keyboard according to the invention. As an example, FIG. 5 to 7show a foil potentiometer that consists of three foils: an upper foil(FIG. 5), a middle foil (FIG. 6) and a lower foil (FIG. 7). These threefoils lie flat over another and are fixed to each other, e.g. bylamination. The middle foil could be replaced by a printed isolationlayer (dielectric) that could be printed onto either the upper or thelower foil.

The upper foil (FIG. 5, 51) is printed with conducting paths made froman electrically well conducting material 52 and conductive paths madefrom a resistive material 53. On one side there is the contact bar 54 inorder to secure the connection to a measuring electronics.

The middle foil (FIG. 6, 61) contains notches (openings) 62 that allow amechanical and electrical contact between the upper and the lower foil.Conductive paths with a low electrical resistance 72 are printed ontothe lower foil (FIG. 7, 71).

FIG. 8 shows an example of a key arrangement that works with the foilpotentiometer from FIG. 5 to 7. These keys are mechanically accentuatedand manouevrable with a click.

FIG. 9 to 12 are similar to FIG. 6 to 8 except for the difference thatone key that is maneuverable along two dimensions requires an extra leadand an additional AD converter. The key 121 can be tilted both inhorizontal and vertical direction and this tilt can be measured.

FIG. 13 shows a key in cutaway view in the non-actuated state. Theactuator 133 has no mechanical contact with the signal detection element(foil potentiometer) 134.

FIG. 14 shows the same key as FIG. 13, however in the actuated state.The actuator 133 lies on the middle of the key 141 and establishes acorresponding electrical contact. When the force is increased, as shownin FIG. 15, then the resting section of the actuator 151 is increased.The total electrical resistance would slightly shrink because of thistiny short-circuit.

FIG. 16 shows how the key has been actuated in a tilted manner. Eventhis leads to a safe contact with this keyboard. The position of thecontact may be determined with the corresponding measurements.

The following applications for the continuously actuatable keys aresuggested: With a numeric telephone keypad arranged similar to FIG. 8 itis possible to enter letters by typing them directly on the key; i.e.pressing onto the left side of the key “2” in order to enter an “A”. Itis also possible to control a cursor arrow key arrangement continuously(FIG. 12, 121).

The advantage of the invention consists in the fact that the keyscanning and an analog control function has been integrated into aunified technology. Any key maneuver leads through a measurement offorce and position of the actuation to a specific electrical resistanceof the output signal, which characterizes the position of the actuation.If a second output signal is evaluated, the applied force of actuationcan also be determined. The necessary technical cost for the proposedsolution is thus significantly lower than with conventional keyboardswith continuous control units.

List of Terms

-   AD0 AD converter-   P1 with S1 signal detection element-   P2 with S2 signal detection element-   P3 with S3 signal detection element-   P4 with S4 signal detection element-   Rp pullup resistor-   51 upper foil-   52 conductive paths with low resistance-   53 conductive paths with high resistance-   54 contact bar with three leads-   61 spacer-   62 openings of spacer-   71 lower foil-   72 material with a low electrical resistance-   73 contact bar-   81 casing-   82 maneuverable keys-   91 contact bar with a total of four leads-   101 round hole for a key that can be tilted in any direction-   121 key that can be tilted in any direction-   131 key caps-   132 key suspension-   133 actuator-   134 signal detection element-   135 carrier plate-   141 small resting section at the key center-   151 large resting section at the key center-   161 small resting section at the key side-   202, 203, 222 electrodes-   211 opening

1. Keyboard with continuously actuatable keys and with an integratedsignal detection element, especially for mobile electronic devices, fordata input and for analog cursor control and selection of functions,wherein the maneuverable mounted keys (82) are equipped with asuspension (132) and are coupled mechanically at their underside with acontinuous conductive path with a high electrical resistance (53)spreading across one or more keys in such a way that after actuation ofkeys the conductive path (53) touches another conductive path with lowelectrical resistance (72) spreading across all keys and ananalog-digital converter AD0 determines the electrical resistance or thevoltage between the conductive path (72) and one end of the conductivepath (53), the measured values being assigned to a specific key andactuation position without ambiguity.
 2. Keyboard according to claim 1,wherein two analog-digital converters AD1 and AD2 are provided thatmeasure the electrical resistance or the voltage drop between theconductive path (72) and both ends of the conductive path (53), themeasured values being assigned to a specific key, to an actuationposition as a point on a line and to the resting section (141, 151, 161)without ambiguity.
 3. Keyboard according to claim 1, wherein theconductive path (53) is connected with one or more calibrationelectrodes CAL1 that allow an exact measurement of the electricalresistance at several positions of the conductive path (53), where thesemeasurements are used as relative reference points for theinterpretation of measured values at the ends of the conductive path(53), so that a precise measurement is possible even under conditions ofproduction-related or temperature-related fluctuations of the totalresistance of the conductive path.
 4. Keyboard according to claim 1,wherein the conductive path (53) of the foil potentiometer as acomponent of a keyboard is divided into several lines lying parallel toeach other, the ends of these lines being connected via a conductivepath with low electrical resistance to the opposite end of the nextline, so that production-related, slight fluctuations of the mountingposition of the keys (82) on the foil potentiometer lead to the samedeviation of the measured values with every key.
 5. Keyboard accordingto claim 1, wherein the foil potentiometer as a component of a keyboardconsists of an upper foil (51), a spacer (61) and a lower foil (71) thatare joined to each other, where conductive paths with a high electricalresistance and optional conductive paths with a low electricalresistance have been printed onto the upper foil (51), and conductivepaths with a low electrical resistance (72) have been printed onto thelower foil (71), and the conductive paths (53) and (72) keep a shortdistance of less than 2 mm in their resting position and touch eachother when the keys (82) are actuated.
 6. Keyboard according to claim 1,wherein three analog digital converters AD1, AD2 and AD3 are providedthat measure the electrical resistance or the voltage drop between theconductive path (72) and three ends of the conductive path (53)Fig. 9),where these measured values are unambiguously assigned to a specifickey, to the actuation position as a point on a circle area and to theresting area (141), (151), (161).
 7. Keyboard according to claim 1,wherein the keys (82) are labeled similar to a numeric telephonekeyboard with a digit or character each and with multiple letters of thealphabet, where depending on the mode digits or letters may be enteredand different letters may be selected depending on the key actuation onthe left side, the center or the right side of the key.
 8. Keyboardaccording to claims 1, where a key (121) is provided that may beactuated at any position of its edge, where the direction of theactuation and the strength of the deflection can be determined as apoint on a circle area by evaluating the relationship of the outputsignals AD1, AD2 and AD3 (FIG. 3) to each other, and where the speed anddirection of a cursor movement can be controlled by manipulating thedirection and tilt of this key (121).
 9. Keyboard according to claim 1,wherein the keys (82) are provided with a key cap (131), a deformable,convex key underside (133) and a flexible suspension (132), so that amechanical pressure from the top actuates a signal detection element(134) lying on a carrier plate (135) at a position that depends fromtheir actuation position and with a resting area (141), (151), (161)that depends on the applied force.
 10. Method for the evaluation ofsignals of a keyboard according to claim 1, wherein a soft touch of thekeys leads to the display of several input alternatives, and one of theinput alternatives is highlighted by means of a cursor, and the positionof the cursor is related to the position of the finger on the key. 11.Method for the evaluation of signals of a keyboard according to claims1, wherein the displayed input alternative is selected after the key isreleased.
 12. Method for the evaluation of signals of a keyboardaccording to claims 1, wherein the displayed input alternative isselected by increased pressure on a key.